Fluid conduit systems and methods for making

ABSTRACT

Multilayer fluid conduits are formed by adhering to a tubular outer surface of a metal pipe, a thermoplastic outer layer. The outer layer permits ends of the multilayer conduit to be joined together in leak-proof fluid conduit systems simply by adhering the conduit ends with compatible thermoplastic fittings. For fire protection systems, the preferred metal is steel, the preferred thermoplastic is CPVC and the preferred adhesive is heat activated. The adhesive coated metal pipe is preheated and the CPVC is extruded onto the outer surface of the heated metal pipe. Through the use of fire resistive CPVC, the multilayer conduit systems of the present invention can be installed in more severe fire threat areas than can existing, all plastic piping, including all CPVC piping systems. The conduit is assembled into systems on site simply by cutting and direct bonding with ordinary, all plastic fittings using appropriate bonding agents such as solvent based adhesives. CPVC fittings are preferred for fire protection systems.

FIELD OF THE INVENTION

The present invention relates to fluid conduit systems, particularlythose suitable for use in fire sprinkler and nozzle systems.

BACKGROUND OF THE INVENTION

Sprinkler system installers typically use metal conduit, either copperor more commonly iron or steel pipe, as supply lines in automaticsprinkler systems. Such metal lines obviously resist fire andtemperature damage better than other structural materials that might beused.

Each metal has relative cost advantages and disadvantages. Typically,piping is provided in fixed lengths and must be cut to size prior toinstallation. Ferrous pipe was then typically threaded in the field andmated with a threaded coupling. The use of threaded couplings in ferrouspiping adds significantly to the labor costs of installing such systems.Copper tubing installs more quickly than ferrous pipe as the cut lengthsof copper can simply be slip-mated with appropriate fittings and thensoldered. However, copper is quite expensive in material cost comparedto ferrous pipe.

Other types of non-threaded mating systems have been developed for metalparticularly steel pipe. For example, crimping systems are known inwhich crimpable fittings can be used to join small diameters of thelightest Schedule 5 steel piping. Other types of mechanical, compressiontype fittings are known which sealingly mate with the exterior ends ofgrooved piping. Still other types of mechanical joining systems employ atubular insert positioned in each open end of a pair of adjoining pipingmembers and an external compression fitting which is applied over theends and the insert to compress the ends against the insert. Suchsystems require either the mechanical shaping and disruption of thesmooth, cylindrical ends of the piping by the addition of grooves,flanges or the like and/or the use of unique and typically expensivecompression fittings.

Certain plastics have gained acceptance for use in residential and, tosome extent, light hazard fire sprinkler systems. Chlorinated polyvinylchloride (CPVC) plastic piping and fittings have been listed byUnderwriters Laboratories. One listed CPVC compound is BLAZEMASTER®brand CPVC of The B. F. Goodrich Co., Cleveland, Ohio. BLAZEMASTER® is aregistered trademark of The B. F. Goodrich Co. Underwriters Laboratorieshas also listed Flameaway brand CPVC pipe and fittings distributed inthe United States by Flameaway Plastics, Inc. of Beverly Hills, Calif.Underwriters Laboratories also lists certain polybutylene sprinkler pipeand fittings for use in residential and light hazard fire sprinklersystems.

Piping made from plastic has proved to be less expensive in materialcost than copper while installation costs have been comparable tocopper. Similar steps are involved in joining together both types ofplastic and copper pipe. However, plastic piping is more flexible thanmetal piping. Support must be provided more frequently with plasticpiping than with metal piping and more frequently with polybutylene thanwith CPVC. This can add sufficiently to both the material costs and thelabor costs of installed plastic piping systems to actually raise thetotal costs of such plastic systems above the costs of metal systems insome installations. Plastic piping for sprinkler systems finds useprimarily in residential installations where the plastic pipe can bemore easily installed through misaligned openings and through and/oraround rafters and joists than can metal piping.

According to recent industry figures, residential sprinkler headsaccount for about fifteen per cent of all sprinkler heads sold. However,because of the greater size of piping and more expensive sprinklerstypically used in light and ordinary hazard installations, the actualdollar value of the residential sprinkler market is estimated to be onlyabout ten per cent or less of the total dollar market for residential,light and ordinary hazard sprinkler installations.

Hybrid plastic/metal piping and couplings have been proposed for fluidconduit systems for many years.

For example, U.S. Pat. No. 5,143,407 to Cokeh refers to a proposal touse copper tubing coated with polyvinyl chloride (PVC) for protectionagainst denting and discloses a variety of copper fittings partiallycoated with PVC for the formation of joints between the ends of lengthsof such multilayer conduit. Cokeh does not indicate how such compositetubing is or could be made or if it has been made. The tubing is joinedwith the fittings by suitable plastic adhesive applied to the plasticoutside surface of the conduit, which bonds to the PVC sleeve formedaround the metal tube portion of the coupling. Compression fit is alsodescribed for securing the pipe ends to the coupling. However, in eachinstance, the use of resilient washers is disclosed to provide aleak-proof fluid seal. This is required because PVC does not bond to thecopper.

Other types of plastic coated pipe have been proposed for otherpurposes. For example, U.S. Pat. No. 3,502,492 discloses theelectrostatic deposition of a light dusting of an epoxy resin upon thesurface of a metal substrate like the outer surface of a metal pipe, theelectrostatic deposition of PVC resin particles upon the surface in aheavier layer and the heating of the substrate to coalesce the PVC andepoxy resins to form a PVC layer adhered to the surface of thesubstrate. Physical structure of the pipes or their joints are notdiscussed.

U.S. Pat. No. 4,481,239 discloses a process for coating metallicsubstrates such as iron pipe in which one or more crosslinking resinsare applied to the pipe surface and heated sufficiently to crosslink andan olefin polymer is applied to the heated, coated substrate as an outerlayer. Structures of the pipe or their joints are not discussed.

U.S. Pat. No. 2,646,822 discloses the use of polyethylene (PE) orpolystyrene as a corrosion resistant external coating for metal pipes.In the only examples shown in that patent, the PE coated metal pipeswere provided with plastic-free, conventionally threaded ends. The endsare shown being received in plastic-coated, metal couplings withplastic-free, internal metal threads to provide continuous lengths ofplastic-coated metal pipe. Coupling at the joint is provided bymechanical engagement of threads on the outside end of the pipe with thethreads inside the metal tubing of the coupling. There is no indicationwhether the plastic layer is adhered to the pipe.

SUMMARY OF INVENTION

In one aspect, the invention is a multilayer fluid conduit systemcomprising: a hollow conduit formed by a hollow length of metal pipehaving a pair of opposing open ends defined by a completely closedtubular outer surface, the open ends of the pipe defining open ends ofthe conduit, a layer of thermoplastic completely covering the tubularouter surface of the pipe and an adhesive layer between the metal pipeand the thermoplastic layer distributed to provide a circumferentialleak-proof seal between the metal pipe and the thermoplastic layer atleast at the open ends of the conduit; and a fitting mounted on one openend of the conduit, the fitting including at least one open endreceiving and overlapping the open end of the conduit, the one open endof the fitting having an exposed, innermost tubular surface ofthermoplastic directly facing and bonded to the thermoplastic layer onthe one open end of the conduit.

In yet another aspect, the invention is a method of making the aforesaidfluid conduit system comprising the steps of: applying an ambienttemperature acting bonding agent to at least one of the thermoplasticlayer exposed on the one open end of the conduit and the exposed,innermost tubular surface of the fitting; and maintaining the conduitand the fitting together with the open end of the fitting receiving andcovering the one end of the conduit until the bonding agent forms theleak-proof sealed joint directly between the conduit and the fitting.

DETAILED DESCRIPTION OF THE DRAWINGS

The foregoing summary as well as the following detailed description ofpreferred embodiments will be better understood when made in conjunctionwith the appended drawings. For the purpose of illustrating theinvention, there is shown diagrammatically in the drawings, embodimentswhich are presently preferred. It should be understood, however, thatthe invention is not limited to the specific embodiments,instrumentalities, elements and methods disclosed in the drawings whichare diagrammatic:

FIG. 1 is a partially broken away length of multilayer conduit accordingto the present invention;

FIG. 2 is a cross-section of an exemplary plastic pipe fitting;

FIG. 3 is a side elevation of part of an automatic ceiling sprinklersystem utilizing multilayer conduits and fittings of FIGS. 1 and 2;

FIG. 4 is a cross-sectional view taken along the lines of 4--4 of FIG.3;

FIG. 5 is a cross-sectional view taken along the lines 5--5 of FIG. 4;

FIG. 6 is a quarter-section side elevation view of a multilayermetal/plastic, tee-shaped threaded adaptor fitting of the presentinvention for mating a conventional threaded fire sprinkler or nozzle ina multilayer conduit system like that of FIG. 3;

FIG. 7 depicts in quarter-section side elevation view, another exemplaryfitting of the present invention with an alternate form of securement tothe forms depicted in FIG. 6;

FIG. 8 depicts in end view yet another exemplary fitting of the presentinvention with an alternate form of securement to those depicted inFIGS. 6 and 7;

FIG. 9 is a schematic view of a process for manufacturing multilayerpipe according to the present invention;

FIG. 10 depicts schematically, in cross-section, an extrusion head forapplying a layer of CPVC resin to the adhesive covered outer surface ofa ferrous pipe;

FIG. 11 depicts schematically an end view of the extrusion pin of theextrusion head of FIG. 10.

FIG. 12 depicts schematically the interior of an air sizing collar onthe extrusion head.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

Certain terminology is used in the following description for convenienceonly and is not intended to be limiting. The words "right", "left","lower" and "upper" designate directions in the drawings to whichreference is made. The words "radial" and "axial" refer to directionsperpendicular to and along the central axis of an object, element orstructure referred to or other designated axis. The words "inwardly" and"outwardly" refer to directions towards and away from, respectively, thegeometric center of the object, element or structure. The terminologyincludes the words above specifically mentioned, derivatives thereof andwords of similar import. Moreover, throughout the drawings, likenumerals are used to indicate like elements.

FIG. 1 depicts diagrammatically an exemplary multilayer fluid conduit ofthe present invention indicated generally at 10. Conduit 10 is formed bya length of hollow metal pipe 12 having a completely closed, tubularouter surface 13 and an opposing closed tubular inner surface 14. Themultilayer fluid conduit 10 further includes a preferably uniformlythick thermoplastic layer 20 which preferably at least essentiallycompletely covers the closed, tubular outer surface 13 of the ferrousmetal pipe 12 from one end 15 to an opposing end 16 of the pipe 12 andconduit 10. An adhesive layer 22 is provided between the metal pipe 12and the thermoplastic layer 20, bonding the thermoplastic layer with theouter tubular surface 13 of the metal pipe 12. The tubular inner andouter surfaces 14 and 13 of the metal pipe 12 are, in this embodiment,uniformly smooth (within manufacturing tolerances) from end 15 to end 16and provide uniform inner and uniform outer diameters to the ferrousmetal pipe 12 from one end of the pipe 15 to the other end 16.

FIG. 2 depicts diagrammatically one fitting 30 of a variety of fittingswhich may be used with the multilayer fluid conduit 10 to assemblemultilayer fluid conduit systems of the present invention like thesystem indicated generally at 40 in FIG. 3.

Returning back to FIG. 2, fitting 30 is a conventional, "tee" shapedsprinkler head adaptor. Fitting 30 includes an integral, thermoplasticbody with first and second opposing tubular open ends 32 and 33. Thetubular open ends 32, 33 are connected by a central tubular branchsection 34 having a third tubular open end 35. A metallic insert 36,internally threaded to receive the threaded end of a fire sprinkler ornozzle or other complementary threaded member, is preferably molded intothe fitting body to form the internally threaded opening of the thirdopen end 35. The exposed, innermost tubular surfaces of the tubular openends 32 and 33 are thermoplastic and again preferably uniformly smoothand of a constant inner diameter.

FIG. 3 depicts diagrammatically a portion of a fire protection system 40utilizing multilayer fluid conduits 10 of the present invention. Theportion of the multilayer fluid conduit system depicted in FIG. 3 isprovided by a plurality of the multilayer fluid conduits 10, connectedtogether, end to end, by a plurality of the tee fittings 30. Hollow endsof adjoining lengths of the multilayer conduits 10 are received in eachof the opposing first and second open ends 32 and 33 of each tee fitting30. The tubular opening 35 of each tee fitting 30 receives the threadedend of a conventional fire sprinkler 38 or nozzle 39. A fire sprinkler38 would have a plug and triggering mechanism holding the plug in placeuntil released. A fire nozzle would be similar to a sprinkler but wouldlack a plug and triggering mechanism. It may even lack a deflector andachieve a water distribution pattern by special shaping of its orifice.

As is best seen in FIGS. 4 and 5, the outer thermoplastic layer 20 ofeach conduit 10 is bonded at 46 to the exposed innermost tubular surfaceof one of the tubular open ends 32 or 33 of the thermoplastic fitting 30(or another suitable fitting) to form a sealed joint between the conduit10 and fitting 30. It should be noted that the central branch section 34defines an exposed, thermoplastic inner tubular surface section of theconduit system 40.

In addition to being joined by thermoplastic fittings like the fitting30, it will be appreciated that according to the present invention, themultilayer conduit 10 can be connected or otherwise combined using otherfittings of standard configuration which are currently used withall-CPVC piping for fire protection systems and with other plasticconduit systems for other uses. These include but are not limited toother forms of sprinkler adapters, straight couplings, elbows, bushings,crosses, caps, plugs, flanges, grooved coupling adapters, and unions,each with slip, spigot or slip and spigot style ends and reduction oruniform internal diameters.

In the preferred embodiment of system 40 configured for fire protection,metal pipe 12 of conduit is of ferrous material, preferably steel. Thethermoplastic layer 20 is preferably of a fire protection ratedchlorinated polyvinylchloride (CPVC) such as BLAZEMASTER® brand CPVC ofThe B. F. Goodrich. The adhesive layer 22 is one which permanently bondsthe CPVC layer 20 to the outer surface 13 of the ferrous metal pipe 12and can adapt to the different coefficients of thermal expansion of thesteel and the CPVC to maintain the bond. The fittings 30 and likefittings for fire protection systems are preferably of a fire protectionrated CPVC such as BLAZEMASTER® brand CPVC with brass threaded inserts36 and are currently available today from various commercial sourcesincluding Central Sprinkler Co. of Lansdale, Pa.

The use of CPVC, in particular, is an important aspect of the preferredembodiment of the invention in several respects. In terms of fireprotection systems, only CPVC and polybutylene have passed industrystandards for fire safety and thus are the only plastics that can beused currently for fire protection conduit systems in virtually alllocals which permit the use of plastic in such systems. However,polybutylene systems have lower maximum ambient operating temperatures(120° F. versus 150° F. for CPVC), are more flexible than CPVC andrequire the provision of heat bonded mechanically crimped joints.Polybutylene heat bonded joints have been proven to be prone to failureafter extended thermal cycling. CPVC can be bonded directly to CPVC toform leakproof joints at ambient temperatures of from about 0° F. to100° F. or more with known, solvent based bonding agents. CPVC can beinstalled with fewer support hangers and in locations with higherambient temperatures and with less structural protection than canpolybutylene. Among plastics commonly molded or extruded, CPVC is one ofthe most difficult to work with. Extrusion temperatures for CPVCpolymers range generally from between about 400° to about 450° F.However, extrusion temperature ranges for particular extrusion equipmentand CPVC formulations may have much narrower ranges, i.e. only about10°-20° F. For example, the BLAZEMASTER® brand CPVC compound has apreferred extrusion temperature range of only between about 415° to 430°F. in the extrusion layout to be described.

The CPVC preferred for extrusion is the conduit outer layer 22 is The B.F. Goodrich Co. BLAZEMASTER® No. 88745 compound. Physical and thermalcharacteristics of that CPVC compound are as follows:

    ______________________________________                                                         BLAZEMASTER ®                                            Property         Brand CPVC     ASTM                                          ______________________________________                                        Specific Gravity "Sp. Gr."                                                                     1.55           D792                                          IZOD Impact Strength                                                                           1.5            D256A                                         (ft. lbs./inch, notched)                                                      Modulus of Elasticity, @                                                                       4.23 × 10.sup.5                                                                        D638                                          73° F., psi "E"                                                        Compressive Strength,                                                                          9,600          D695                                          psi "o"                                                                       Poisson's Ratio "O"                                                                            .35-.38        --                                            Working Stress @ 73° F.                                                                 2,000          D1598                                         psi "S"                                                                       Hazen Williams   150            --                                            Factor "C"                                                                    Coefficient of Linear                                                                          3.4 × 10.sup.-5                                                                        D696                                          Expansion in/(in °F.) "e"                                              Thermal Conductivity                                                                           0.95           D177                                          BTU/hr/ft.sup.2 /°F./in "k"                                            Flash Ignition   900            D1929                                         Temperature "°F."                                                      Limiting Oxygen  %60            D2863                                         Index "LOI"                                                                   Electrical Conductivity                                                                        Non Conductor                                                Extrusion Temperature (approx.)                                                                414-425° F.                                                                           N/A                                           Heat Distortion  217° F. --                                            Temperature "°F."                                                      ______________________________________                                    

Further information about CPVC resins used in BLAZEMASTER® No. 88745CPVC compound is provided in U.S. Pat. No. 4,412,898 which isincorporated herein in its entirety.

Very thin, cold rolled steel, for example SAE C1010 twenty gauge steel,is presently preferred for the ferrous metal pipe 12 of the multilayerconduit 10 of the present invention as it offers cost benefits not foundin other metals. Other ferrous metals that might be used includegalvanized steel, stainless steel or a steel with higher carbon valuesthan C1010 to minimize wall thickness through increased strength.

Adhesion of the preferred CPVC material with the ferrous pipe 12 isnecessary as CPVC will not directly bond to metal even when extruded ina melted form onto the metal. Adhesive layer 22 is provided to preventthe likelihood of water wicking between the metal pipe 12 and the CPVCouter layer 20 covering the pipe 12 when the conduits 10 are connectedtogether into a fluid conduit system. The adhesive layer 22 further isalso sufficiently elastic to accommodate the different thermal expansioncoefficients of the metal pipe 12 (about 6 to 7×10⁻⁶ /F.°) and CPVCouter layer 20 (about 3.4×10⁻⁵ /F.°) to prevent failure of the bondbetween the CPVC and the ferrous pipe in use. If the conduit 10 is to becapable of being cut to any length for use, the adhesive layer mustextend entirely around and entirely along the pipe 12 from end to end. Aseries of separate, individual adhesive rings might be provided alongthe pipe but a continuous adhesive layer running the entire length ofthe pipe completely around the pipe is much preferred for versatility.If the conduit 10 is to be used without further cutting, it is onlynecessary to provide an adhesive layer around either end of the pipe 12extending away from the pipe end a distance sufficient to create anenduring waterproof seal between the pipe 12 and CPVC layer 20 aroundeach of the ends of the pipe 12.

Preferred bonding materials for the aforesaid steel pipe andBLAZEMASTER® brand CPVC compound are The B. F. Goodrich Co. Adhesive No.A1718B and a two part system, Chemlok® 485 and Curative 44, of the LordCorporation, Elastomer Products of Erie, Pa.

The B. F. Goodrich Co. A1718B is considered a solvent based primer. Itis a liquid which includes a proprietary mix of methyl ethyl ketone,toluene, butyl alcohol, ethanol and isopropyl alcohol, and propyleneoxide.

The Chemlok® 485/Curative 44 ingredients constitute a two componentelastomeric adhesive. The Chemlok® 485 includes xylene, methyl ethylketone and ethyl benzene in a proprietary combination the Chemlok®Curative 44 includes xylene, aromatic polyisocyanate,4,4'-diphenylmethane diisocyanate, ethyl benzene and diphenylmethanediisocyanate in a proprietary combination. The two are mixed insuggested proportions of 100 parts by weight Chemlok® 485 with 6-10parts by weight Curative 44.

Each is preferably sprayed on the outer surface 13 of the pipe 12without dilution in an amount sufficient to yield a thickness of abouttwo to three mils when dry.

Preferably, multilayer conduit 10 is provided in outer diametersconforming to nominal piping or tubing outer dimensions, e.g. Schedules40 and/or 80 (ASTM F438) to be used with nominally sized fittings. Allthicknesses of the metal pipe 12, thermoplastic layer 20 and adhesivelayer 22 of the multilayer conduit 10 would be only sufficiently thickto provide the strength and rigidity needed for a safe, leak-proofconduit system for the use or uses to which such conduit system isapplied.

Outer diameters of the multilayer conduits 10 preferably will beconventional corresponding to the outer diameters of nominal pipe size(NPS) piping or tubing, e.g. from three-quarters of an inch to at leastfour inches in diameter, for use with corresponding, nominally sizedfittings. ASTM Schedule 40 and Schedule 80 fittings are standard sizesfor plastic used in fire protection conduit systems. Plastic fittingsfor use with plastic piping or tubing having nominal sizes of about twoinches or less can be used in fire protection systems with Schedule 40dimensions (ASTM F438), although Schedule 80 dimensions (ASTM F439) withheavier walls may also be used. A plastic fitting for use with plasticpiping or tubing having a nominal pipe size of more than two inches mustconform to Schedule 80 dimensions for fire protection system use. Otherstandard dimensions for pipes and fittings might be used for other usesof the conduit system. For example, standard ASTM pipe and fittingschedules range from Schedule 5 to Schedule 100 in size.

At least for fire protection conduit systems, the preferred CPVC layer20 is provided in a wall thickness of less than 0.1 inch, suggestedlyless than 0.08 and preferably of only about 0.04 inches althoughthicknesses as thin as about 0.020 inch and as much as 0.075 inch arealso being contemplated for this use.

For fire sprinkling systems, the ferrous pipe 12 of the multilayer fluidconduit 10 preferably is very thin cold rolled steel having a wallthickness of less than 0.1 inch, suggestedly less than 0.08 inch andeven 0.06 inch and preferably approximately only about 0.04 inch (e.g.0.042 inch), although thicknesses of between about 0.035 and 0.065inches are being contemplated for use with nominal pipe sizes ("NPS") ofup to at least three inches. The thinnest threaded steel pipe wallthickness permitted by standard ASTM schedules for fire sprinklersystems is believed to be 0.087 inches. The thinnest CPVC wall thicknesspermitted for fire sprinkler use is 0.085 inches for three-quarter inchnominal pipe size. For nominal pipe sizes of one inch or more, CPVC wallthickness must be more than 0.100 inches.

Piping and tubing are normally sized by specified outer diameters. Thefittings with which they are used are internally sized in relation tothe standard outer diameters specified for the piping and tubing to bereceived by the fittings. For standard fitting sizes, conduits 10 of thepresent system will have at least marginally larger inner diameters thanwould all plastic pipe and even standard steel pipe. For example,one-inch (NPS) Schedule 10 steel pipe, which is widely used for firesprinkler systems, has an actual inner diameter of 1.097 inches and awall thickness of 0.109 inches. Although this pipe is designed for rollgrooving, it is sufficiently thick to be threaded. The thinnest steelpipe used in fire protection systems is Schedule 5. It is commerciallyavailable in nominal pipe sizes of between one and two inches. All havenominal wall thicknesses of 0.065 inches. Such thin-walled pipe isnon-threadable. ASTM Designation: A795-93, "Standard Specification for .. . Steel Pipe for Fire Protection Use," sets forth schedules of NominalPipe Sizes, actual outer diameters and nominal wall thicknesses, forthreadable Schedule 10 and 40 steel pipe, which are as follows:

                  TABLE                                                           ______________________________________                                                            Schedule 10                                                                              Schedule 40                                             Outside    Nominal Wall                                                                             Nominal Wall                                   NPS      Diameter   Thickness  Thickness                                      Designator                                                                             (Inches)   (Inches)   (Inches)                                       ______________________________________                                        1/2      0.840      --         0.109                                          3/4      1.050      0.083      0.113                                          1        1.315      0.109      0.133                                          1-1/4    1.660      0.109      0.140                                          1-1/2    1.900      0.109      0.145                                          2        2.375      0.109      0.154                                          2-1/2    2.875      0.120      0.203                                          3        3.500      0.120      0.216                                          3-1/2    4.000      0.120      0.226                                          4        4.500      0.120      0.237                                          5        5.563      0.134      0.258                                          6        6.625      0.134      0.280                                          ______________________________________                                    

The wall thicknesses for CPVC pipe are similar to threadable steel pipeat the smallest nominal pipe sizes, e.g. 0.087 inch versus 0.085 inchfor 1/2 inch (NPS) steel pipe and CPVC tubing, respectively. In allcases, the ferrous metal pipe of the multilayer conduit of the presentinvention will be thinner than the thinnest nominal wall thicknessprescribed for the thinnest pipe of the same nominal diameter previouslyusable in fire protection systems.

Wall thickness requirements increase more quickly for CPVC ranging from0.107 inch for one-inch diameter (NPS) tubing (1.101 inch actual innerdiameter) to 0.300 inches for three inch diameter (NPS) tubing. It isexpected that the increased inside diameter that can be provided byusing the multilayer conduit 10 of the present invention with standardCPVC fittings would provide approximately 4% more water flow thanconventional thin-walled steel pipe systems (less than Schedule 10) and8% more water flow than traditional Schedule 10 and 40 steel pipesystems for approximately the same nominal pipe sizes. The increasedcapacity will be even greater in comparison to all-CPVC systems,particularly in sizes greater than one inch. This effective increase ininside diameter will, in some cases, permit a contractor to reduce pipesize for a sprinkling system, thereby saving additional labor andmaterial for the contractor.

If the outer diameter of the multilayer conduit 10 is fixed by the innerdiameter of the conventional fittings with which it is used, the outerdiameters of the metal pipe 12 will depend upon the thicknesses of thethermoplastic and adhesive layers 20 and 22. As a result, the metal pipeof the present invention generally will be of non-standard outer andinner diameters.

The multilayer conduit 10 of the present invention has all of thefabrication advantages of all plastic piping. Multilayer conduit 10 ofthe present invention can be cut to any length in the field using commonwheel cutters. The cut end is preferably deburred and the CPVC layer maybe chamfered for ease of assembly. No threading or grooving or otherdisruption of the conduit ends or of the metal pipe in particular isrequired for joint formation. An ambient temperature acting bondingagent is simply applied around the end of the conduit 10 on the exposedthermoplastic layer 20 and/or on the exposed innermost surface of thefitting, which is formed by the exposed thermoplastic layer, receivingthe end of the conduit. The pieces are joined by inserting the conduitend in the fitting open end and twisting to distribute the bondingagent. The resulting bonded joint will cure and be pressure supportivewithin minutes using the indicated preferred bonding agents. Thethermoplastic outer layer 20 has the further advantage of protecting theoutside of the metal pipe 12 from corrosion.

One step solvent cements produced by the IPS Corp. of Gardena, Calif.,and the Oatey Company, Cleveland, Ohio, are the preferred ambienttemperature acting bonding agents to join the above described CPVCcoated conduits 10 and CPVC fittings 30 and provide joints which remainleak-proof and integral at pressures of at least 875 psi or more. TheIPS formulation is known as Central Sprinkler CSC-300 Solvent Cement. Itis also known as WELD-ON 723 (Modified for BLAZEMASTER® CPVC Pipe). TheOatey formulation is called "Oatey Medium Red BLAZEMASTER® CementCPVC-Low VOC." These bonding agents are applied directly, withoutdilution and are suitable for use at ambient temperatures, i.e. at sometemperature(s) between about 0° and 120° F. Each is described as amixture of CPVC resin and organic solvents including tetrahydrofuran,methyl ethyl ketone, cyclohexanane and acetone. Each is applied withoutdilution and cures at room temperature (e.g. about 0--about 120° F.).

FIG. 6 depicts diagrammatically in a quarter-section view a multi-layermetal/plastic threaded sprinkler adaptor type tee shaped fitting of thepresent invention, indicated generally at 130, that can be used forincreased thermal protection in higher challenge fire locations. Theimproved fitting 130 includes an inner, conventional thermoplastic,preferably CPVC fitting 30, such as fitting 30 of FIG. 2, and asurrounding metal shell indicated generally at 132. Metal shell 132 canbe stamped, shaped and folded around the tee-shaped fitting 30 andsecured about the fitting 30 by any of a variety of ways including, butnot limited to, brazing indicated generally at 134 or banding indicatedby band 136. Other forms of securement are shown in FIGS. 7 and 8. InFIG. 7, pairs of facing flanges (one being depicted at 138) are providedon a modified metal shell 132' of yet another fitting embodiment 130'with opening(s) 140 to receive a conventional fastener 142, which mightbe a rivet, screw or bolt portion of a nut and bolt combination. FIG. 8is an end view of yet another fitting embodiment 130" in which outwardlyturned and inwardly turned opposing flanges 138", 139" of metal shell132" overlap one another and lock around the fitting 30. Each of shells132, 132' and 132" provides a metal layer at least substantiallyentirely covering the otherwise outer surface of fitting 30 sufficientlyto measurably improve the ability of the fitting 30 to withstand heat.

FIG. 9 depicts in block diagram form, suggested steps for fabricatingthe multilayer conduit 10. Preferably, the thin-walled steel pipe 12 isprovided preformed in individual, cut standard lengths. The steel pipeis cleaned of any residual scale and other contaminant(s) and degreasedat step 60 and then cleaned of degreaser, for example, by forced airevaporation at step 62. Next, an appropriate adhesive material 24 isapplied to the completely closed tubular outer surface 13 by anysuitable means in an adhesive applying step 64. Spraying the entireouter surface of the metal pipe 12 is preferred but the adhesivematerial 24 may be brushed or rolled onto the pipe 12 or the pipe 12 maybe dipped. The adhesive material 24 is then dried in a drying step 66.For the disclosed preferred adhesives, drying is preferably accomplishedby heating at a temperature below the activation temperature, forexample, about 150° F., to sufficiently eliminate solvent carriers fromthe adhesive to permit the pipe with adhesive coating or layer to behandled. The adhesive coated pipe will hereinafter be identified byreference numeral 12'. The pipe with adhesive material layer 12' can bedried by heating to a temperature as hot as the adhesive will permitwithout activating. This is about 340°-350° F. for The B. F. Goodrichadhesive but only about 250° F. for the Lord Co. system.

The pipe with adhesive coating 12' is passed through an extrusion head88 as shown in FIG. 10. The preferred adhesive material layer 24 ispreheated by a set of preheaters 85a, 85b, 85c and by the tooling of thehead 88 to an activation temperature above the drying temperature,desirably above 350° F., in a heat activating step 68 just prior toapplication of the melted CPVC. The indicated adhesives are heated toabout 360° F. or more for activation. The Lord Co. system can be heatactivated at a temperature below 350° F., if desired. The adhesive 24 ispreferably heat activated before physically entering the extrusion head88 but could be heat activated within the head as well. By preheatingthe surface of the pipe 12' at the entrance to the head 88, the pipe 12'can still be handled from outside the head to advance it through thepreheaters and the head. Preheating the pipe 12' helps to maintain thetemperature of the extruded plastic. CPVC 21 or other extrudablethermoplastic is applied in a tubular layer 20 in an extruding step 70.

The multilayer conduit 10 can be moved through the extrusion head 88 ina variety of ways including pushing, pulling or, preferably, acombination of initially pushing and subsequently pulling, for example,using pinch wheels (not depicted).

The conduit 10 may be treated in a sizing step 72 in which the outsidesurface is finished to achieve a more exact and uniform sizing of theouter diameter of the CPVC layer 20 and conduit 10. The outer diameterof the conduit 10 is believed to be sizable in a number of ways whichare standard for sizing plastic tubing including but not limited tomechanical rolling, vacuum sizing or a combination of such processes, aswell as by positive air pressure as will be described with respect toFIG. 12.

If mechanically cut lengths of steel pipe 12 are fed sequentially intothe extrusion head 88, the ends of such pipe would be slightly inwardlyrolled or "dimpled" from the cutting process. This slight reduction inpipe diameter at the pipe ends is within normal manufacturing tolerancesfor such pipe. Although slight, the variation in dimension should bedetectable by a proximity detector or the like with the pipes 12 buttedend to end. Also, it would be possible to track the location of the pipeends by providing an encoder or encoders on one or more servoscontrolling wheels feeding pipe through the extrusion head with a sensoror sensors which can detect the beginning and end of the pipe.Alternatively the pipes could be fed into the extrusion head with gapsbetween each pipe. A space of about 1/32" or more could be developedbetween adjoining ends of adjoining lengths of pipe, depending upon themethod of feed. The space will be spanned by a continuous tube of theCPVC material, which should collapse between the pipes for lack ofinternal support to identify the pipe ends. Since these changes would bemore pronounced than the rolled pipe ends, it is believed that other,different sensors (e.g. ultrasonic, magnetic, electric and/or opticalmeans of detection) also can be used to locate the pipe ends exiting theextrusion head 88. The precut lengths of metal pipe 12 can thus beidentified, separated from one another and the ends of the resultingmultilayer conduits 10 cleaned of excess CPVC in a finishing step 74.

FIG. 10 depicts diagrammatically the major tooling components of apreferred extrusion head 88 for applying CPVC material to adhesivecoated metal pipe 12'. A conventional extruder is partially depicted andindicated generally at 80. The extruder 80 includes a reservoir of CPVCwhich is heated and fed under pressure in a conventional manner througha coupling 82 into a feed conduit 86 of the head and into the extrusionhead 88 itself. The CPVC passes through an opening 87a in a bushing 87of the head 88 and into a compression chamber 96 defined between aninner tubular surface of bushing 87 and an outer surface of an extrusionpin 90. Extrusion pin 90 has a central bore 91 (in phantom) to receiveand pass the adhesive coated metal pipe 12' and a feed channel 92 on itsouter surface to receive CPVC from the feed conduit 86. The extrusionhead 88 further includes a mandrel 94 supporting the pin 90 from itsupstream end. If desired, the downstream end of the pin 90 can supportedby a knife edge spider extended between the pin 90 and the bushing 87 orbetween a die 98 attached to the bushing 87 and the pin 90. The bushing87 surrounds the proximal end of the pin 90 and the die 98 surroundingthe distal end of the pin 90.

Feed channel 92 has two symmetric halves, one of which is indicated at92a and is seen in FIG. 10. The hidden half is a mirror image on theother side of the pin 90. Both halves 92a, 92b are seen in phantom inFIG. 11, an end view of the pin 90. Each feed channel portion 92a, 92bspirals helically from opening 87a to an opposing side of the pin 90,180° around the pin 90 away from the opening 87a. Preferably, the feedaxis of the extruder 80 and the central axes of the coupling 82 and feedconduit 86 are coplanar with one another and with feed channels 92a, 92bto minimize stagnation and shear. Each feed channel portion 92a, 92bsmoothly and progressively diminishes in cross-sectional area from anessentially true semi-circle directly adjoining opening 87a to nocross-sectional area, where the feed channel 92a and its mirror 92b meeton the opposite side of the pin 90 from opening 87a. The pin 90 includesa generally cylindrical portion 90a supporting the channel 92. Pin 90 isthereafter inwardly tapered down in a cone-shaped portion 90b to asecond, smaller diameter cylindrical portion 90c, having a wallthickness of less than 0.1 inch and an inner diameter only about 60 milslarger than the outer diameter of the steel pipe 12. If desired aplurality of radially inwardly and longitudinally extending knife edgescan be provided within the bore of pin 90 to help keep the pipe 12'centered as it feeds from the end of pin 90. The inner diameter of thebushing 87 below the channel 92 is about 0.3 inches greater than thediameter of the pin 90 immediately below the channel 92. This differenceessentially defines the radial dimension of the annular compressionchamber 96. The die 98 has a tapered portion 98a facing the taperedportion 90b of pin 90 and a uniform diameter bore 98b receiving theuniform diameter distal end 90c of pin 90. The uniform inner diameterbore 98b in die 98 might be, for example, about 0.09 to about 0.12inches greater than the outer diameter of the extreme distal 90c of thepin 90 to extrude a tube of CPVC with a wall thickness of about 45 to 60mils in order to apply about a forty mil thickness of CPVC or otherthermoplastic to pipe 12'. The pipe 12' is passed through the extrusionhead at a speed greater than the speed at which the CPVC compound isbeing extruded. Preferably, the speed is controlled to stretch the CPVCcompound to approximately 40 mils, which is slightly less than theoriginal extruded thickness.

To control the temperature of the CPVC compound, heating zones aremaintained in or on the extrusion head tooling and elsewhere. Preferablyseparate, independently controlled heating zones are maintained on thecoupling 82, the feed conduit 86, the head housing 84 above the bushing87, and the bushing 87 itself below feed conduit 86. In addition, eachof the preheaters 85a, 85b, 85c is preferably separately controlledupstream from the head 88 to preheat the pipe 12' and activate theadhesive coating 22 immediately prior to passing through the extrusionhead 88. The extrusion head heat zones are preferably maintained atabout 365° F. to permit some shear heating of the CPVC compound as itpasses from the extruder 80 and through the head 88.

The orientation and progressive reduction in cross-sectional area of thechannel portions 92b, 92a are very important to the success of the CPVCextruding step. Portion 92a and its mirror image counterpart 92b moveresin more quickly to the opposite side of the pin 90 than the resinwould have arrived there without the channel 92 to prevent unevencooling of the resin circumferentially around the pin 90. The channelhalves 92a, 92b lie in a common plane with the centerline of the feedconduit 86 and bushing opening 87a. The depth of each channel half 92a,92b is reduced linearly as each channel half extends from the bushingopening 87a (0° position on the pin 90) to the opposite side of pin 90(180° position). In addition, the cylindrical portion of the pin on thedownstream side of the groove is further cut back from about halfwayalong each channel half 92a, 92b (i.e. about 90° and 270° positions) tothe far side of the pin 90 (i.e. the 180° position), again generallylinearly beginning at about each halfway position (i.e. about 90° and270° positions) to a depth of about 0.090 inches at the opposite side(i.e. 180° position) of the pin 90. The generally uniform cooling of themelted CPVC is very important as it prevents the formation of anoticeable weld or knit line or a high stress concentration where suchline might normally be located on the side of the pin 90 oppositeopening 88a.

Preheating the adhesive coated pipe 12' to near the temperature of theextruded CPVC (e.g. within at least about 50° F. and preferably towithin less than 50° F. of the temperature of the applied CPVC) assistsin maintaining temperature of the CPVC compound in the extrusion head88, in a preferred temperature processing range. In the extrusion head88, that range is only about 15° F. (about 415° to about 430° F.). Thepreferred CPVC compound is resistive to being pulled to the preferredthinness due to its viscousness from chlorination. The preferredcompound tends to tear if permitted to cool to 410° F. or below andtends to burn or gall if permitted to exceed about 450° F. If pulled tooquickly through the tooling, the CPVC can be overheated by the frictionand burn. The ideal temperature for discharging the CPVC would be justunder or about 450° F. It is believed the above-described arrangementdelivers CPVC compound to the pin 90 (or pipe 12') at about 430° F. Oneinch diameter pipe is currently being passed at a rate of about thirtyto thirty-five feet per minute through the described tooling with theidentified CPVC compound, steel pipe and heat activated adhesives.

FIG. 12 shows a proposed arrangement for sizing. A tubular sizing collar100 is mounting in the exposed end of die 98. The collar includes aninner passageway 102 through which the plastic coated conduit 10 passeswhen exiting the die 98. An annular manifold 104 is provided within thecollar coupled with a feed conduit 106 through which a pressurizedsource of air indicated by arrow 108 or other appropriate gas can befed. A plurality of individual bores 110 extend radially inwardly fromthe manifold 104 into the inner passageway and define a ring of air jetswhich surround any conduit 10 passing through the extrusion head 88.Thickness of the thermoplastic layer 22 is controlled by a combinationof operating parameters including feed rate of the pipe 10', feed rateand temperature of the CPVC compound or other extruded thermoplastic andpressure of the air or other gas blown through the bores 110.

The multilayer conduit and conduit systems of the present inventionoffer significant benefits in costs and ease of use over other knownmetal, plastic or composite metal/plastic conduit systems, particularlyin fire protection systems. The preferred multilayer conduit of thepresent invention provides greater strength and greater rigidity atreduced wall thickness than can be provided by all plastic piping. Themultilayer conduit of the present system invention can be coupledtogether into systems as easily as all plastic systems without the firedanger or cost associated with installing brazed copper systems or theexpense of installing all steel systems. The multilayer conduit of thepresent system permits the installation of conduit systems with lessskilled labor and without the expense of threading equipment, flaringequipment, torches, thermal bonding or crimping equipment or otherexpensive, mechanical fitting coupling systems.

Because the present system does not require the provision of threads orother disruptions in the inner and outer tubular surfaces of the ferrousmetal pipe 12 or the multilayer conduit 10 or the compression of theends of the pipe or conduit, steel piping thinner than steel piping everknown to have been previously used in such systems can now be used forlight weight and cost savings while still providing the rigidity ofmetal with full integrity to pressures of 875 psi and more. The conduitof the present invention is expected to be the first conduit systememploying plastic, which is designed for use in ordinary hazardoccupancies as defined by National Fire Protection Association (NFPA)13. However, it is believed that the advantages of the preferredcomposite system will lead to much greater acceptance and use in lighthazard systems where all metal piping presently predominates ininstalled fire protection systems. In particular, it is expected thatthe hanger requirements for the preferred composite conduit 10 of thepresent invention will be at least as favorable as steel (maximumspacing of fifteen feet between supports). Because of its greatlyreduced weight, conduit of the present invention should be able to besafely spaced at greater distances between supports (e.g. sixteen feetup to possibly twenty feet) to further reduce the installation costwhile permitting greater installation flexibility.

The multilayer conduit of the present invention has the advantage ofbeing able to be used with a host of existing CPVC fittings and, throughthose fittings, being coupled to other copper, steel and traditionalplastic (e.g. PVC, ABS, etc.) conduit systems and piping.

While preferred embodiments of the invention have been disclosed andcertain modifications thereto suggested, still other modifications andchanges will occur to those of ordinary skill in the art. For example,while CPVC is preferred for the fittings and adhered CPVC is preferredfor the conduits for sprinkler systems, other polymers might be used.Other extrudable, adherable, ambient temperature bondable polymers whichmight be used include, in addition to CPVC, polyvinyl chloride (PVC),acrylonitrile-butadienestyrene (ABS), polyurethanes (both polyesters andpolyethers), and blends thereof with one another and with CPVC. All areextrudable, adherable to metal and solvent bondable. In distinguishingbetween PVC and CPVC, any PVC polymer more than 57% by weight chlorineis considered a chlorinated PVC.

The preferred CPVC thermoplastic layer complements the preferred steelpipe in other ways. The preferred CPVC is quite strong itself. The CPVCouter layer 22 protects the steel pipe 12 from external corrosion. Sincesuch piping is dry or contains standing (non-flowing) water untilactivated, little internal corrosion typically occurs in such systems.Thus, even thinner steel wall can be used for fire protection than forother, more active (fluid flowing) conduit systems. Other polymers mightbe used with ferrous metal or with other metal pipes previously threadedfor uses other than fire protection.

The invention is not limited to the specific preferred embodiments andalternate embodiments disclosed, but is intended to cover allembodiments set forth in the appended claims.

We claim:
 1. A multilayer fluid conduit system comprising:a hollowconduit formed by a hollow length of metal pipe having a pair ofopposing open ends defined by a completely closed tubular outer surface,the open ends of the metal pipe defining open ends of the conduit, alayer of thermoplastic completely covering the tubular outer surface ofthe metal pipe, and an adhesive layer between the metal pipe and thethermoplastic layer distributed to provide a circumferential leak-proofseal between the metal pipe and the thermoplastic layer at least at theopen ends of the conduit; a fitting mounted on one open end of theconduit, the fitting including at least one open end receiving andoverlapping the one open end of the conduit, the one open end of thefitting having an exposed, innermost tubular surface of thermoplasticdirectly facing and bonded to the thermoplastic layer on the one openend of the conduit so as to form a leak-proof sealed joint at the oneend of the conduit directly between the conduit and the fitting.
 2. Theconduit system of claim 1 wherein the metal pipe has a tubular innersurface and wherein the tubular outer and inner surfaces of the metalpipe are uniformly smooth from end to end of the metal pipe.
 3. Theconduit system of claim 1 wherein the material of the metal pipe issteel.
 4. The conduit system of claim 1 wherein the metal pipe has awall thickness insufficient to support threads.
 5. The conduit system ofclaim 1 wherein the metal pipe has a wall thickness less than 0.08inches.
 6. The conduit system of claim 5 wherein the metal pipe has awall thickness of about 0.06 inches or less.
 7. The conduit system ofclaim 6 wherein the metal pipe has a wall thickness of about 0.04inches.
 8. The conduit system of claim 1 wherein the metal pipe has awall thickness of less than 0.08 inches in nominal pipe sizes up tothree inches.
 9. The conduit system of claim 1 wherein the conduitthermoplastic layer has a wall thickness of less than 0.08 inch.
 10. Theconduit system of claim 1 wherein the conduit thermoplastic layer has awall thickness of about 0.04 inch.
 11. The conduit system of claim 1wherein the conduit thermoplastic layer has a wall thickness of betweenabout 0.02 inch and 0.075 inch.
 12. The conduit system of claim 11wherein the metal pipe has a wall thickness less than 0.08 inch.
 13. Theconduit system of claim 11 wherein the metal pipe has a wall thicknessof up to 0.06 inches.
 14. The conduit system of claim 11 wherein themetal pipe has a wall thickness of about 0.04 inch.
 15. The conduitsystem of claim 11 wherein the metal pipe has a wall thickness ofbetween about 0.035 and about 0.065 inch.
 16. The conduit system ofclaim 15 wherein the tubular outer and inner surfaces of the metal pipeat the ends of the conduit lack surface variations which would enableinterference engagement with a mating fitting.
 17. The conduit system ofclaim 1 wherein the adhesive layer bonds the thermoplastic layer withthe metal pipe only after being heated to a temperature above 300° F.18. The conduit system of claim 1 wherein the adhesive layer completelyencircles the tubular surface of the metal pipe and extends along themetal pipe sufficiently from ends of the metal pipe to form an unbrokenannular waterproof seal between the metal pipe and the thermoplasticlayer.
 19. The conduit system of claim 1 wherein the thermoplastic layerof the conduit comprises CPVC.
 20. The system of claim 19 wherein thethermoplastic layer of the conduit consists essentially of CPVC.
 21. Thesystem of claim 19 wherein the innermost surface of the fittingcomprises CPVC.
 22. The system of claim 21 wherein the innermost surfaceof the fitting consists essentially of CPVC.
 23. The system of claim 20wherein the innermost surface of the fitting consists essentially ofCPVC.
 24. The system of claim 20 wherein the innermost surface of thefitting comprises CPVC.
 25. The system of claim 23 wherein the one openend of the conduit and the one end of the fitting each lack structurewhich provides interference engagement to couple the conduit with thefitting.
 26. The system of claim 1 wherein the fitting further includesan outer metal layer at least substantially entirely covering thefitting.
 27. The system of claim 1 further comprising an automatic firesprinkler fluidly coupled with the fitting.
 28. The system of claim 1further comprising a fire nozzle fluidly coupled with the fitting. 29.The system of claim 1 wherein the wall thickness of the metal pipe andthe wall thickness of the thermoplastic layer of the conduit is eachless than 0.08 inches.
 30. The system of claim 29 wherein the combinedwall thickness of the metal pipe and the thermoplastic layer of theconduit is up to 0.10 inches.
 31. The conduit system of claim 1 furthercomprising:an ambient temperature acting bonding agent between thethermoplastic material layer on the conduit and the exposed, innermosttubular surface of the fitting effective to form a leak-proof sealedjoint encircling the one end of the conduit directly between the conduitand the fitting.
 32. A method for making the fluid conduit system ofclaim 1 from the fitting and the hollow conduit, comprising the stepsof:applying an ambient temperature acting bonding agent to at least oneof the thermoplastic material layer exposed on the one open end of theconduit and the exposed, innermost tubular surface of the fitting; andmaintaining the conduit and the fitting together with the tubular openend of the fitting receiving and covering the one end of the conduituntil the bonding agent forms the leak-proof sealed joint directlybetween the conduit and the fitting encircling the one end of theconduit.
 33. A method for making the fluid conduit of claim 27 systemfrom the fitting and the hollow conduit, comprising the stepsof:applying an ambient temperature acting bonding agent to at least oneof the thermoplastic material layer exposed on the one open end of theconduit and the exposed, innermost tubular surface of the fitting; andmaintaining the conduit and the fitting together with the tubular openend of the fitting receiving and covering the one end of the conduituntil the bonding agent forms the leak-proof sealed joint directlybetween the conduit and the fitting encircling the one end of theconduit.